Retinal capillary fragments from rhesus monkey, bovine, and human autopsy retinas have been placed in tissue culture. These vessels behave as explants, producing a uniform line of polygonal cells by the thirtieth day. Autoradiography has demonstrated that the proliferating elements of the original capillaries are the mural cells or intramural pericytes. Electron micrographs depict the mature cultured cells as containing organs typical of mural cells in situ and cultured smooth muscle cells. Using gas liquid chromatography and a radioimmunoassay for aldose reductase, the presence of the polyol pathway has been established in the cultured mural cells. The possible role of this metabolic pathway in the etiology of mural cell loss and diabetic neovascularization is discussed.